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<h1>Advanced API</h1>

<div id="filing">Filed under Development</div>
<div id="index">Return to the <a href="index.html">index</a>.</div>
<div id="home"><a href="http://htmlpurifier.org/">HTML Purifier</a> End-User Documentation</div>

<p>
  <strong>Warning:</strong> This document may be out-of-date. When in doubt,
  consult the source code documentation.
</p>

<p>HTML Purifier currently natively supports only a subset of HTML's
allowed elements, attributes, and behavior; specifically, this subset
is the set of elements that are safe for untrusted users to use.
However, HTML Purifier is often utilized to ensure standards-compliance
from input that is trusted (making it a sort of Tidy substitute),
and often users need to define new elements or attributes. The
advanced API is oriented specifically for these use-cases.</p>

<p>Our goals are to let the user:</p>

<dl>
    <dt>Select</dt>
    <dd><ul>
        <li>Doctype</li>
        <!-- <li>Filterset</li> -->
        <li>Elements / Attributes / Modules</li>
        <li>Tidy</li>
    </ul></dd>
    <dt>Customize</dt>
    <dd><ul>
        <li>Attributes</li>
        <li>Elements</li>
        <!--<li>Doctypes</li>-->
    </ul></dd>
</dl>

<h2>Select</h2>

<p>For basic use, the user will have to specify some basic parameters. This
is not strictly necessary, as HTML Purifier's default setting will always
output safe code, but is required for standards-compliant output.</p>

<h3>Selecting a Doctype</h3>

<p>The first thing to select is the <strong>doctype</strong>. This
is essential for standards-compliant output.</p>

<p class="technical">This identifier is based
on the name the W3C has given to the document type and <em>not</em>
the DTD identifier.</p>

<p>This parameter is set via the configuration object:</p>

<pre>$config->set('HTML', 'Doctype', 'XHTML 1.0 Transitional');</pre>

<p>Due to historical reasons, the default doctype is XHTML 1.0
Transitional, however, we really shouldn't be guessing what the user's
doctype is. Fortunantely, people who can't be bothered to set this won't
be bothered when their pages stop validating.</p>

<h3>Selecting Elements / Attributes / Modules</h3>

<p>HTML Purifier will, by default, allow as many elements and attributes
as possible. However, a user may decide to roll their own filterset by
selecting modules, elements and attributes to allow for their own
specific use-case. This can be done using %HTML.Allowed:</p>

<pre>$config->set('HTML', 'Allowed', 'a[href|title],em,p,blockquote');</pre>

<p class="technical">The directive %HTML.Allowed is a convenience feature
that may be fully expressed with the legacy interface.</p>

<p>We currently support another interface from older versions:</p>

<pre>$config->set('HTML', 'AllowedElements', 'a,em,p,blockquote');
$config->set('HTML', 'AllowedAttributes', 'a.href,a.title');</pre>

<p>A user may also choose to allow modules using a specialized
directive:</p>

<pre>$config->set('HTML', 'AllowedModules', 'Hypertext,Text,Lists');</pre>

<p>But it is not expected that this feature will be widely used.</p>

<p class="technical">Module selection will work slightly differently
from the other AllowedElements and AllowedAttributes directives by
directly modifying the doctype you are operating in, in the spirit of
XHTML 1.1's modularization. We stop users from shooting themselves in the
foot by mandating the modules in %HTML.CoreModules be used.</p>

<p class="technical">Modules are distinguished from regular elements by the
case of their first letter. While XML distinguishes between and allows
lower and uppercase letters in element names, XHTML uses only lower-case
element names for sake of consistency.</p>

<h3>Selecting Tidy</h3>

<p>The name of this segment of functionality is inspired off of Dave
Ragget's program HTML Tidy, which purported to help clean up HTML. In
HTML Purifier, Tidy functionality involves turning unsupported and
deprecated elements into standards-compliant ones, maintaining
backwards compatibility, and enforcing best practices.</p>

<p>This is a complicated feature, and is explained more in depth at
<a href="enduser-tidy.html">the Tidy documentation page</a>.</p>

<!--
<h3>Unified selector</h3>

<p>Because selecting each and every one of these configuration options
is a chore, we may wish to offer a specialized configuration method
for selecting a filterset. Possibility:</p>

<pre>function selectFilter($doctype, $filterset, $tidy)</pre>

<p>...which is simply a light wrapper over the individual configuration
calls. A custom config file format or text format could also be adopted.</p>
-->

<h2>Customize</h2>

<p>By reviewing topic posts in the support forum, we determined that
there were two primarily demanded customization features people wanted:
to add an attribute to an existing element, and to add an element.
Thus, we'll want to create convenience functions for these common
use-cases.</p>

<p>Note that the functions described here are only available if
a raw copy of <code>HTMLPurifier_HTMLDefinition</code> was retrieved.
Furthermore, caching may prevent your changes from immediately
being seen: consult <a href="enduser-customize.html">enduser-customize.html</a> on how
to work around this.</p>

<h3>Attributes</h3>

<p>An attribute is bound to an element by a name and has a specific
<code>AttrDef</code> that validates it. The interface is therefore:</p>

<pre>function addAttribute($element, $attribute, $attribute_def);</pre>

<p>Example of the functionality in action:</p>

<pre>$def->addAttribute('a', 'rel', 'Enum#nofollow');</pre>

<p>The <code>$attribute_def</code> value is flexible,
to make things simpler. It can be a literal object or:</p>

<ul>
    <!--<li>Class name: We'll instantiate it for you</li>
    <li>Function name: We'll create an <code>HTMLPurifier_AttrDef_Anonymous</code>
        class with that function registered as a callback.</li>-->
    <li>String attribute type: We'll use <code>HTMLPurifier_AttrTypes</code>
        to resolve it for you. Any data that follows a hash mark (#) will
        be used to customize the attribute type: in the example above, 
        we specify which values for Enum to allow.</li>
</ul>

<h3>Elements</h3>

<p>An element requires certain information as specified by
<code>HTMLPurifier_ElementDef</code>. However, not all of it is necessary,
the usual things required are:</p>

<ul>
    <li>Attributes</li>
    <li>Content model/type</li>
    <li>Registration in a content set</li>
</ul>

<p>This suggests an API like this:</p>

<pre>function addElement($element, $type, $contents,
    $attr_collections = array(); $attributes = array());</pre>

<p>Each parameter explained in depth:</p>

<dl>
    <dt><code>$element</code></dt>
    <dd>Element name, ex. 'label'</dd>
    <dt><code>$type</code></dt>
    <dd>Content set to register in, ex. 'Inline' or 'Flow'</dd>
    <dt><code>$contents</code></dt>
    <dd>Description of allowed children. This is a merged form of
        <code>HTMLPurifier_ElementDef</code>'s member variables
        <code>$content_model</code> and <code>$content_model_type</code>,
        where the form is <q>Type: Model</q>, ex. 'Optional: Inline'.
        There are also a number of predefined templates one may use.</dd>
    <dt><code>$attr_collections</code></dt>
    <dd>Array (or string if only one) of attribute collection(s) to
        merge into the attributes array.</dd>
    <dt><code>$attributes</code></dt>
    <dd>Array of attribute names to attribute definitions, much like
        the above-described attribute customization.</dd>
</dl>

<p>A possible usage:</p>

<pre>$def->addElement('font', 'Inline', 'Optional: Inline', 'Common',
    array('color' => 'Color'));</pre>

<p>See <code>HTMLPurifier/HTMLModule.php</code> for details.</p>

<div id="version">$Id: dev-advanced-api.html 1651 2008-04-05 18:37:08Z Edward $</div>

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